878 research outputs found
New insights from bacterial biomarkers into the oxic/anoxic transition of the Holocene Black Sea
No full textUnusual distributions of long-chain alkenones and tetrahymanol from the highly alkaline Lake Van, Turkey
No full textLong-chain C37 to C40 alkenones with di-, tri-, and tetra-unsaturation are very abundant in sediment trap material and Holocene to Late Pleistocene core samples from the Earth's largest soda lake, Lake Van (Turkey). Thus, the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments. The observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra-unsaturated compounds, especially the C37:4 methyl ketone. Their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation. Using published U37K calibrations, no reliable absolute temperatures were obtained for the Lake Van samples. Accordingly, marine sea surface temperature determinations based on long-chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded. The presence of tetrahymanol and gammacer-3-one in the Lake Van materials is attributed to organic matter contributions of ciliates. The relative abundance of long-chain alkenones and of tetrahymanol/gammacer-3-one is considered to reflect changes in the environmental conditions, in particular in the hydrological setting. We suggest that times of pronounced stagnation are recognised by very high tetrahymanol/gammacer-3-one concentrations together with drastically increased stanol/stenol ratios, and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions
A new straight-chain hydrocarbon biomarker associated with anaerobic methane cycling
No full textC-13-depleted E and Z n-tricos-10-enes are prominent biomarkers in an anaerobic microbial mat at Black Sea methane seeps. These n-alkenes co-occur with archaeal irregular C-25 isoprenoid hydrocarbons, namely 2,6,10,15,19-pentamethylicosanc (PMI) and -enes (PMI Delta). Low delta C-13-values (-73 and -77 parts per thousand) for n-tricosenes and PMI imply the anabolism of methane carbon by their source biota. The n-tricosenes apparently originate from microorganisms closely associated with, if not identical to isoprenoid-producing, methane-metabolizing Archaea. Methane-seep deposits of Tertiary to Jurassic ages showed the absence of n-tricosenes, but C-13-depleted n-tricosane (delta C-13 as low as -87 parts per thousand), a plausible diagenetic product, was observed in enhanced concentrations in 7 out of 9 samples studied. It is proposed that a preference of n-tricosane over the enveloping n-alkanes may provide a specific hydrocarbon fingerprint for the anaerobic cycling of methane in ancient settings. (C) 2001 Published by Elsevier Science Ltd
Membrane lipid patterns typify distinct anaerobic methanotrophic consortia
No full textThe anaerobic oxidation of methane (AOM) is one of the major sinks of this substantial greenhouse gas in marine environments. Recent investigations have shown that diverse communities of anaerobic archaea and sulfate-reducing bacteria are involved in AOM. Most of the relevant archaea are assigned to two distinct phylogenetic clusters, ANME-1 and ANME-2. A suite of specific 13C-depleted lipids demonstrating the presence of consortia mediating AOM in fossil and recent environments has been established. Here we report on substantial differences in the lipid composition of microbial consortia sampled from distinct compartments of AOM-driven carbonate reefs growing in the northwestern Black Sea. Communities in which the dominant archaea are from the ANME-1 cluster yield internally cyclized tetraether lipids typical of thermophiles. Those in which ANME-2 archaea are dominant yield sn-2-hydroxyarchaeol accompanied by crocetane and crocetenes. The bacterial lipids from these communities are also distinct even though the sulfate-reducing bacteria all belong to the Desulfosarcina/Desulfococcus group. Nonisoprenoidal glycerol diethers are predominantly associated with ANME-1-dominated communities. Communities with ANME-2 yield mainly conventional, ester-linked diglycerides. ANME-1 archaea and associated sulfate-reducing bacteria seem to be enabled to use low concentrations of methane and to grow within a broad range of temperatures. Our results offer a tool for the study of recent and especially of fossil methane environments
C-0661: Smithfield, Utah, Walter R. Michaelis/Orin G. and Gwenevere H. Miles residence. Sec 27 T 13N R 1 E, 404 Canyon Road. Built 1906
No full textC-0661: Smithfield, Utah, Walter R. Michaelis/Orin G. and Gwenevere H. Miles residence. Sec 27 T 13N R 1 E, 404 Canyon Road. Built 190
Biofilm exopolymers control microbialite formation at thermal springs discharging into the alkaline Pyramid Lake, Nevada, USA
No full textCalcium carbonate precipitation and microbialite formation at highly supersaturated mixing zones of thermal spring waters and alkaline lake water have been investigated at Pyramid Lake, Nevada. Without precipitation, pure mixing should lead to a nearly 100-fold supersaturation at 40°C. Physicochemical precipitation is modified or even inhibited by the properties of biofilms, dependent on the extent of biofilm development and the current precipitation rate. Mucus substances (extracellular polymeric substances, EPS, e.g., of cyanobacteria) serve as effective Ca2+-buffers, thus preventing seed crystal nucleation even in a highly supersaturated macroenvironment. Carbonate is then preferentially precipitated in mucus-free areas such as empty diatom tests or voids. After the buffer capacity of the EPS is surpassed, precipitation is observed at the margins of mucus areas. Hydrocarbon biomarkers extracted from (1) a calcifying Phormidium-biofilm, (2) the stromatolitic carbonate below, and (3) a fossil 'tufa' of the Pleistocene pinnacles, indicate that the cyanobacterial primary producers have been subject to significant temporal changes in their species distribution. Accordingly, the species composition of cyanobacterial biofilms does not appear to be relevant for the formation of microbial carbonates in Pyramid Lake. The results demonstrate the crucial influence of mucus substances on carbonate precipitation in highly supersaturated natural environments
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